1. Field of the Invention
The present invention relates to apparatus and process for the polymerization of alpha-olefins using Ziegler type catalysts consisting of liquid and solid catalyst components whereby fouling resulting from solid cocatalyst injection is eliminated.
2. Related Art
In stirred liquid phase Ziegler polymerizations of alpha-olefins fouling of solid catalyst injection nozzles has been a continuing problem which reduces on stream time and requires periodic reactor shutdown to clear the nozzles. In order to minimize fouling the solid and liquid components of the Ziegler catalyst are fed separately, however, once both components are present together in the reaction zone the chance contact of the liquid cocatalyst component with the solid cocatalyst component exiting a nozzle or inlet is sufficient to result in polymer fouling of the nozzle. The liquid portion of Ziegler type catalyst does not present a fouling problem per se and is easily injected into the system.
Rapid dispersion of the solid cocatalyst within the reaction mass is the key to preventing fouling of the nozzle or reactor surfaces. It would appear that introduction of the solid cocatalyst below the liquid surface would provide the best means of obtaining this result except for the problem of fouling widely observed in the art in these systems.
Various approaches have been used to reduce or eliminate fouling of the solid cocatalyst nozzles. For example, mechanical roding devices are often employed, but are unsatisfactory since plugs are pushed into the reactor which cause downstream process and product problems. U.S. Pat. No. 3,285,900, Houser, et al. uses a continuous loop tubular reactor where the cocatalysts and reaction mass are continuously moved through the reaction zone in the highly turbulent flow range. U.S. Pat. No. 3,330,818, Derby, uses two opposed impellers each of which force the reaction mass toward the other with the inlet points for catalysts and reactants between the two opposed impellers. U.S. Pat. No. 3,694,423, Smith, et al. uses a loop reactor with a specific solid cocatalyst delivery system employing a plurality of transport zones and a reciprocating piston to force the solid cocatalyst into the polymerization zone. U.S. Pat. No. 3,726,845, Nickerson, inhibits plugging of the solid cocatalyst feed line by alternating catalyst slurry with diluent through the same line.
It is an advantage of the present invention that the solid cocatalyst slurry is fed below the liquid level of the reaction mass thereby avoiding "plating" of the reactor surface above the liquid surface, which occurs with vapor space feeding of the solid cocatalyst. It is a further advantage of the present invention that fouling of the solid cocatalyst feed line is eliminated. A particular feature of the present invention is that the solid cocatalyst slurry is fed continuously at the desired rate, thereby assuring a controlled and predictable Ziegler catalyst in the reaction mass at all times. These and other advantages and features of the present invention become apparent from the following disclosures.